Anatomical and Morphological Adaptations

Abstract

Metcalfe (1983) lists the following anatomical and morphological characters as being xeromorphic:

• 1. Leaves may be small, sometimes with the margins inrolled, as in Erica cinerea and E. tetralix.

• 2. Characteristically, in many xerophytes the leaves become detached, and water loss is thereby reduced.

• 3. In some taxa, such as Salicornia spp., leaves are absent and photosynthesis is carried out by the stem. In some cases the stem chlorenchyma may then consist of palisade cells.

• 4. Water loss may be controlled by the stomata, as in Flourensia thurifera. The stomata are often numerous and frequently protected by being depressed, surrounded by flanges of cuticle, etc.

• 5. The leaf cells, especially the epidermal cells, are often conspicuously smaller than corresponding cells in mesophytes and hydrophytes. However, there are exceptions, such as, for example, the enlarged water-storage cells in the epidermis or hypodermis of Peperomia incana and P. pereskiaefolia.

• 6. The cuticle is often above average thickness, as are also the walls of the epidermal cells, especially the outer periclinal walls. This is well developed in members of the Cactaceae.

• 7. Many xerophytes have hairy leaves and are generally to be found in members of the Caryophyllaceae, Chenopodiaceae, Compositae, Ericaceae and Solanaceae. In some xeromorphs these are air-filled or of a distinctive type. It was once believed that the indumentum gave a physiological advantage to xerophytes by shielding the stomata and thereby reducing transpiration loss. In many cases it has been experimentally demonstrated that such an hypothesis is false.